As LSI circuits are increasing in density, the line width of circuits of semiconductor devices is becoming finer. To form a desired circuit pattern onto a semiconductor device, a method of reducing and transferring, by using a reduction-projection exposure apparatus, onto a wafer a highly precise original image pattern (mask, or reticle, in particular, when used in a stepper or a scanner) formed on a quartz is employed. The highly precise original image pattern is written by using an electron beam writing apparatus, in which a technology commonly known as electron beam lithography is used.
An electron beam writing apparatus performs writing by causing a deflector to deflect an electron beam. The role of beam deflection by using the deflector includes adjusting the shape and/or size of a beam shot, adjusting a shot position, and blanking control for switching between a beam ON state and a beam OFF state.
When a blanking voltage applied to a blanking deflector is at a first predetermined value (e.g., 5 V), an electron beam is deflected such that the whole of the beam is blocked by a blanking aperture member, and thus enters the beam OFF state. When the blanking voltage is at a second predetermined value (e.g., 0 V), the beam passes through an aperture of the blanking aperture member, and thus enters the beam ON state.
A blanking circuit for applying a voltage to the blanking deflector includes an analog circuit, such as digital-to-analog converter (DAC) amplifier. If a fault occurs in the analog circuit, the blanking voltage will fail to be set at a predetermined value, causing an error. An error in blanking voltage leads to an insufficient dose or the tilt of the axis of a beam, resulting in a reduction in writing accuracy. The detection of faults in analog circuits is often delayed. For example, such a fault may fail to be detected in an electron beam writing apparatus, and may be identified during inspection of patterned masks for defects or in the next or following process (e.g., wafer processing) after several weeks. In such a case, a large number of defective masks would be produced before identification of the fault.
An insufficient dose causes the dimensions of a write pattern to change. Whether a fault has occurred in the blanking circuit can be determined based on the pattern dimensions. However, a similar change in pattern dimensions is caused by a failure of a shaping deflection circuit for adjusting the size of a beam shot. It is therefore difficult to determine the occurrence of a fault in the blanking circuit.